The invention concerns a valve drive device and an internal combustion engine with a valve drive device.
A valve drive device for an internal combustion engine with at least one camshaft which has at least one cam element with at least one multi-track cam, which is intended to be axially displaced by a maximum displacement path is known from DE 10 2011 050 484. The valve drive device has a latching mechanism which is intended to lock a changeover to a central cam track, but which is unlatched by the cam element at high speeds so that the cam element exceeds the desired axial displacement.
The invention is based, in particular, on the task of providing a valve drive device with which a safe switchover between valve strokes can be achieved at high camshaft speeds.
The invention is based on a valve drive device, in particular for an internal combustion engine with at least one camshaft which has at least one cam element with at least one multi-track cam, which is intended to be axially displaced by a maximum displacement path.
It is proposed that the valve drive device comprises a limiting mechanism intended to limit, in at least one operating condition, the displacement path of the cam element to a switching path for a switching operation, thereby safely limiting axial displacement of the cam element and preventing overshooting of a desired axial displacement, thus achieving safe switching between valve strokes even at high camshaft speeds. In this context, a “multi-track cam element” is understood to mean a cam element with at least two partial cams, each of which forms a cam track for actuating a gas shuttle valve, the partial cams providing different valve lift and/or valve timing. In this context, a “maximum displacement path” is understood to mean a displacement path of the cam element in which the cam element is displaced from an axial position, in which an outermost cam track is provided for actuating the gas exchange valve, to an axial position, in which an opposite outermost cam track is provided for actuating the gas exchange valve. In this context, a “switching path for a switching operation” is understood to mean an axial displacement of the cam element with which the cam element is displaced from an axial position, in which a cam track for actuating the gas exchange valve is provided, to an axial position, in which a directly adjacent cam track for actuating the gas exchange valve is provided. In particular, the switching path for a switching operation is at most equal to the maximum displacement path and, if a cam of the cam element has at least three cam tracks, less than the maximum displacement path. One length of the switching path for a switching operation corresponds in particular to one length of the maximum displacement path divided by a number that is one less than a number of cam tracks.
It is further proposed that the valve drive device comprises a positive locking element at least connected to the cam element and intended for positive connection to the limiting mechanism, thus allowing a simple construction of the valve drive device to be achieved.
It is also proposed that the limiting mechanism should have a stop element with two opposite stop surfaces for the positive locking element, so that the stop element can be used to limit the displacement to one switching path in one axial direction and one opposing axial direction, and a simple design of the valve drive device can be achieved.
Furthermore, it is proposed that the stop surfaces be spaced apart in such a way that any displacement is limited to the value of the distance between adjacent cam tracks, so that a limitation of the displacement path to a switching path for switching between adjacent cam tracks can be limited in a simple way.
It is also proposed that the limitating mechanism should include an auxiliary actuator to displace the stop element so that one switching element can be used to limit the displacement path to one switching path for switching adjacent cam tracks if more than two cam tracks of a multi-track cam are used.
It is also proposed that the valve drive device has a switching actuator for axially displacing at least one cam element, which comprises at least one switching element which is in permanent operative connection with the cam element, and a drive for axially displacing the switching element designed to be decoupled from the switching element so that, after the switching operation has been completed, when the limiting mechanism blocks further displacement of the cam element, the drive can be decoupled from the switching element and thus a precise actuation of the drive in order to limit the displacement of the cam element to the switching path can be dispensed with.
It is also proposed that the switching element be permanently connected to the positive locking element, thus eliminating the need for an additional component to engage with the switching element and simplifying the design of the valve drive device.
It is also proposed that the switching actuator should include a slipping clutch designed to decouple the switching element and the drive from each other, thus providing a simple design for decoupling the switching element from the drive.
It is also proposed that the valve drive device should include a spindle for transmitting a driving force from the drive to the switching element, which is connected to the drive via the slipping clutch, thus providing a simple design for decoupling the switching element from the drive.
It is also proposed that at least one multi-track cam should have at least three cam tracks, allowing the limiting mechanism to be used with particular benefit for safe switching between adjacent cam tracks.
Furthermore, the invention concerns an internal combustion engine with a valve drive device corresponding to the invention, which reliably limits an axial displacement of the cam element and prevents overshooting of a desired axial displacement, thus achieving safe switching between valve strokes even at high camshaft speeds.
Further advantages can be seen in the description of the figures below. The figures show an example of the invention. The figures, the description of the figures and the claims contain numerous features in combination. Experts will also consider the features individually and combine them into other useful combinations.